Este texto tiene como tema los cambios sociodemograficos habidos en el Alentejo (region localizada al sur de Portugal). A traves de un conjunto de indicadores de poblacion, veremos como este territorio registro durante el periodod 1950-2001 dinamicas demograficas diferenciadas y contradictorias...This paper will analyze the social changes that took place in the region of Alentejo (In Southern Portugal) on the last decades. Using some statistical data from the national population census, the author will present and describe a complex reality of different and opposite demographic tendencies, like, for instance, the opposition between a recent urbanization and a progressive depopulation. In three decades this region has suffered a huge and profound demographic transformation.